G8 THE CHEMISTRY OF THE FARM. 



sumed alone. In the foraier case the non-nitrogenous 

 ingredients of the food supply the heat and force de- 

 manded by the animal body, in the latter case the 

 albuminoids have to meet every requirement. 



If an adult animal receives the small quantity of al- 

 bumhioids and ash constituents necessary to supply the 

 waste of tissue, the whole of its remaining wants may 

 probably be met by supplies of carbo-hydrates and 

 of fat. 



The ash constituents present in the food are the same 

 as those found in the animal body ; all that is accom- 

 plished by the animal is to select from the supply those 

 of which it is in want. 



2. Digestion. — The object of digestion is to bring the 

 solid constituents of the food into a form suitable for ab- 

 sorption into the blood. Of the carbo-hydrates of the food 

 some, as sugar, are already soluble and diffusible, and need 

 no digestion ; others, as starch and cellulose, are naturally 

 insoluble. The digestion of carbo-hydrates commences 

 with the action of the saliva, which has the property of 

 converting starch into sugar. This action, in the case of 

 ruminants, is prolonged by the temporary sojourn of the 

 food in the first two stomachs, and its return to the mouth 

 in chewing the cud. The further solution of starch and 

 cellulose is effected in the intestines, partly by the pan- 

 creatic juice, which has a powerful action on starch, and 

 partly by the fermentive processes which take place. 



The albuminoids of the food are attacked by the gastric 

 juice of the stomach (the fourth stomach of ruminants), 

 and converted into peptones, bodies similar to albuminoids 

 in composition, but which, unlike them, are diffusible 



